The invention relates to impact-resistant materials, in particular of the type suitable for ballistic protection.
The widespread availability of guns, rifles, pistols knives and other assorted equipment which characterises the last part of this century, has given rise to an increased demand for materials to protect both humans and equipment against these hazards.
Historically, the development of weapons has been followed by a respective development of armour systems to defeat them. A more advanced, penetrative weapon, or a cutting implement harder than the armour, require heavier armour to defeat it. Typically, heavier armour has a number of significant disadvantages. In the case of body or vehicle armour, higher weight reduces mobility. Heavier armour also tends to be bulkier and less flexible, which is a problem in particular with armoured vests. In general, armouring material is expensive and using more, increases both weight and cost of the product.
Armour producers were among the first to use advanced, high-strength lightweight materials such as fabrics comprised of aramid fibres, ultra-high molecular weight polyethylene fibres, carbon fibres and liquid crystal polyester fibres, as well as high density, lightweight, hard materials, such as titanium, alumina oxide-, boron carbide-, silicon carbide- and metal matrix-ceramics, and ultra hard metals.
In order to achieve the desired protective properties, selected materials have often been combined with each other in layer-like fashion.
One of the most successful multi-layer types of materials for use against high-energy impacts, such as those caused by high-velocity rifle bullets, employs a strike-face comprising the hardest available material within weight/cost constraints in a multiple-tile configuration. The tiles can be made of ceramic, metal, plastic, metal alloys, rapid solidification (RSM) materials or metal or ceramic foams. The strike-face layer is applied (e.g. by mechanical fixing, lamination or gluing) upon a stiff energy absorbing material which may be a metal or plastic layer, or layers of softer material such as the high-tech fabrics mentioned above, or combinations thereof. These fabrics must be consolidated by a lamination process employing various resins, e.g. phenolic-, polyester-, vinylester-, epoxy-, polyethylene-, polycarbonate- or other suitable resins.
The most commonly employed material illustrating the state of the art strike face would be boron carbide ceramic tiles. Known tile shapes are square, rectangular, hexagonal or diamond. The tiles are arranged side by side, in a multiple tile configuration with mating edges, adhered to an ultra-high molecular weight polyethylene (UHMW PE) laminate. The thickness and density of both the ceramic and laminate are engineered to be sufficient to defeat the specified threat.
Functionally, when the ceramic tile (strike-face) is impacted it destroys the penetrative ability of the impactor by radical deformation and, should the impactor have sufficient remaining energy to pass beyond the ceramic tile, the minor remaining energy is absorbed by the laminate. The intimate adhesion of the ceramic to the laminate is of primary importance since unsupported ceramic is by nature brittle and requires a rigid backing support. The absence of such a support would cause the resistance to decrease significantly, leading to failure to meet the desired level of impact-resistance. Another requirement of such a construction is for the mating edges to be placed tightly against one another, in case the impactor strikes the joint of two or more tiles. Such a construction is necessarily rigid and inflexible, if it is to satisfy accepted specifications, for example, United States National Institute of Justice (USNIJ) 0101.03 Ballistic Standard or other National Standards for ballistics or impact, such as the United Kingdom""s Police Scientific Development Branch (PSDB) Stab-resistant Body Armour Test Procedure October 1993.
U.S. Pat. No. 3,867,239 is directed to an armour construction with an array of platelets contoured edges wherein the construction uses an overlapping stepped joint construction to improve the protection at the joints. This construction reduces flexibility.
There is therefore a need for a material utilising an appropriate strike face, whilst at the same time remaining flexible.
The invention is particularly, but not exclusively, applicable in the ballistic protection field. The invention is largely based on the construction of a supportive layer behind the, strike face tiles which is made to be of non-ballistic properties, yet still have a high resistance to local deformation.
In this regard, it should be noted that the material xe2x80x9cbeing of non-ballistic propertiesxe2x80x9d means that the flexible material layer (which may itself comprise one or more layers), is by itself unable to meet any international ballistics standard. The lowest internationally recognised ballistics standard can, for the purposes of this invention, be regarded as the xe2x80x9cCEN 1063 standard for bullet resistance of glazing: handguns and riflesxe2x88x92BRI calibre 0.22 inch (5.59 mm) long riflexe2x80x9d. The flexible material layer of non-ballistic properties according to the invention thus has ballistics resistance properties which are in the range of about 2% to 50% of the aforementioned lowest ballistic standard, preferably between about 5% and 50% of said standard, more preferably between about 10% and 35% of said standard, and most preferably between 15% and 25% of said standard. As such, the flexible material would not have any recognised or useful ballistic resistance by itself.
According to the invention, there is provided a flexible impact- or blast-resistant composite material.
Due to the complementary mating edges, the tiles are easily placed in an abutting relationship without a gap therebetween.
The flexible material acts as a support for the strike face tiles, while maintaining desired flexibility properties.
By xe2x80x9cstrike-facexe2x80x9d is meant that side of the material which is intended to resist an attack. This is the layer which is first struck by the impactor.
By xe2x80x9chigh resistance to local deformationxe2x80x9d is meant a material which produces an indentation of 10 mm or less when subject to a local deformation test as hereinafter described.
By xe2x80x9cintegral withxe2x80x9d is meant any manner by which the tiles are made one with the flexible material, including chemical and mechanical attachments including combinations thereof, such as adhering and/or encapsulating.
The invention also relates to impact resistant tiles. Such tiles are suitable for use with ballistic or impact resistant materials.
The tiles may have a shape such that when a plurality of identical tiles are suitably placed adjacent each other they form a continuous surface. It is also possible to make mating combinations of tiles having different shapes.
The tiles may be planar with one of the following shapes: square (a), rectangular (b), hexagonal (c), diamond (d), double hexagonal (e), butterfly (f), chevron (g) half-trapezium (h), stretched hexagon (i), trapezium (j), rectangle with curved shorter ends curved in same direction (k), T-shape (l), segment of circle with radii in the form of curves with the same radius as the circle (m), butterfly (n), or complex rhombic.
The shapes of the tiles may preferably have corners greater than 90 degrees and when the tiles are arranged side by side, have a maximum of three tiles at an intersection.
The tiles may be non-planar and have one of the following shapes: cylindrical (p), pyramid (q), truncated pyramid (r) or angle shape (s).
Suitably the tiles may comprise ceramic tiles, preferably boron carbide ceramic.
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.